A man lies in an Ebola isolation centre set up by the Liberian health ministry in a school in Monrovia. The WHO has been criticised for a slow reaction to the epidemic. Photograph: John Moore/Getty Images

The magnitude of the Ebola outbreak in west Africa, which has killed more than 1,000 people, has been vastly underestimated and will require “extraordinary measures, on a massive scale” if it is to be contained, the World Health Organisation has warned.

Such steps, said the WHO, had been taken in “recognition of the extraordinary measures needed, on a massive scale, to contain the outbreak in settings characterised by extreme poverty, dysfunctional health systems, a severe shortage of doctors and rampant fear”.

Ernest Bai Koroma, Sierra Leone’s president, painted a stark picture of the outbreak in the country with the highest death toll, admitting that the government’s initial response had been too slow but saying more help could have come from countries with greater resources and expertise.

After observing a minute’s silence in memory of those who died, a sombre-looking president said:“I wasn’t happy with the response because we have all been slow, and this is a crisis that requires quick action in terms of response. What we can do as a government, I believe we have done. We look forward to the international community to increase their response.”

“This is a call we’re now making to the world because we need treatment centres. And in the treatment centres, we need clinicians that require specialised training. We don’t have that. And if people are dying the response should be an extraordinary response. We must limit bureaucracy.”

Sierra Leone had received less than $2m in direct international funding, Koroma said, although millions more had been channelled through aid organisations.

“Unlike infections such as influenza or tuberculosis, Ebola is not airborne,” said Dr Isabelle Nuttall, WHO’s director of global capacity alert and response. “It can only be transmitted by direct contact with the body fluids of a person who is sick with the disease.”

Nuttall said the risk of Ebola transmission on flights was so low that the WHO did not consider airports to be a particular danger.

• This article was amended on 19 August 2014. An earlier version said that Sierra Leone “has no labs capable of testing for the virus”. In fact there are currently two testing facilities, a mobile lab in Kailahun run by MSF and a centre in Kenema supported by Metabiota and the Sierra Leone government.